I'd stop running for your school. Your coach sounds absolutely stupid. He should not be a coach. He knows nothing about running. I went from 28:18 to 26:46 8K XC. I'll probably run a new PR tomorrow. I'll post it if I do. I made my improvements by running my easy runs easier and my hard runs harder. I use a heart rate monitor to be sure of it. My team always makes fun of me when I strap on my monitor because they I know that I won't be running with them, I'll be somewhere behind them. With the cool temps and low humidity though, my regular run pace is about 6:45, recovery 7:15. Depending on me physically, and the weather, and the shape I'm in, usually my recovery pace at 60% is closer to 8. My numbers are changing though, I might be getting set up for a break through. My resting HR was down to 49 bpm last month, it might be lower now. My team usually runs about 7 min/mile for most of their mileage. So when I'm running 7:05 or 7:15 I'm still within shouting distance for the first few miles, so that's why they make fun of me and say things like, we're only running a little bit faster, but that little bit slower is what will decide if I have an ok workout or a great workout the next day. 10 seconds a mile doesn't sound like much, but after 10 miles a day 7 days a week it makes a difference.